Controller of scanning apparatus

A controller of a scanning apparatus comprising:

• a gain compensation circuit for compensating the image data of a plurality of scan lines, each scan line including a plurality of pixels, characterized in that said gain compensation circuit comprises a vertical compensation circuit for performing vertical compensation computations on said plurality of scan lines, and said plurality of pixels of each scan line are compensated with a same vertical gain value and;
• wherein said vertical compensation circuit comprises a vertical gain latch for receiving and storing said vertical gain value, a vertical register for storing said vertical gain value, a vertical counter electrically connected to said vertical register to issue a vertical pointer V.sub.pointer to allow synchronization of said scan lines, and a first multiplier electrically connected to said vertical register for receiving an original image data and said vertical gain value, wherein said horizontal compensation circuit comprises an offset latch for receiving and storing said shading compensation offset value, a horizontal gain latch for receiving and storing said shading compensation gain, a horizontal counter for issuing a horizontal pointer H.sub.pointer to said offset latch and said horizontal gain latch to allow synchronization of said pixels for each scan line, an adder electrically connected to said first multiplier and said offset latch, and a second multiplier electrically connected to said adder and said horizontal gain latch.